Conventionally, devices in which a circuit assembly including a circuit board on which various electronic components are mounted is accommodated in a case are known as devices for energizing and de-energizing in-car electric components.
In such devices, the electronic components mounted on the circuit board are small and have superior functionality.
However, these electronic components have a relatively large heat generation, and thus if heat generated by the electronic components stay in the case, there will be a risk that the temperature in the case increases and the performance of the electronic components accommodated in the case decreases.
Accordingly, as an example of various structures for discharging the heat generated by the circuit board or the electronic components, a circuit assembly 111 as shown in FIG. 7 is conceivable that has a configuration in which a heat discharging member 130 is provided on that surface of a circuit board 112 that is opposite to the surface on which an electronic component 115 is provided.
On the other hand, as shown in FIGS. 6 and 7, it is also conceivable that an opening 113 is formed in a region of the circuit board 112 that corresponds to the electronic component 115, a plurality of busbars 120 are provided on that surface of the circuit board 112 that is opposite to the surface on which the electronic component 115 is provided, and terminals 117 of the electronic component 115 are connected to the busbars 120 exposed through the opening 113. By configuring an electric power circuit with the plurality of busbars 120, it is possible to flow a high current through the electric power circuit.
However, when the electronic component 115 is connected to the plurality of busbars 120 via the opening 113 formed in the circuit board 112, an adhesive agent 135 for bonding the heat discharging member that is laid (layered) on the surfaces of the busbars 120 that are opposite to the circuit board 112 may enter a gap S between adjacent busbars 120, and may get into contact with a lower surface of a main portion 116 of the electronic component 115, as shown in FIG. 7. In such a situation, if the adhesive agent 135 expands due to the heat generated by the circuit board 112 or the electronic component 115, or adversely contracts by being cooled, the electronic component 115 will be pushed or drawn by the adhesive agent 135, possibly causing a connection failure such as a crack in a connection section between the terminal 117 and the busbar 120.
The technique disclosed in the present description was made in view of the above-described circumstances, and it is an object thereof to provide a circuit assembly and an electrical junction box that have high connection reliability.